JB 2000 transformer

[238]

I have a one tube, 3-500, amp i am rebuilding. It originally had a SSB220 transformer in it, but it passed away. Had a JB2000 transformer installed. I thought some one might know the voltage of the different wires. The guy just cut the other wires off. The big yellow wire is cut off also. The amp works as is, but i am going to rebuild the power supply. The caps & diodes. I was hoping some one might know the color code. Thanks 238

 

[nomadradio]

Don't remember having that on file, but I'll poke about and see what's to be had. The four thick black wires on the right side of the pic should be the two 120-Volt primary windings. If the number tags are still on each of those four wires, the amplifier schematic should sort out how they're connected. Pretty sure the two red wires at the lower left are the 1000-Volt (or so) HV winding.

The fat green wires on the left would be the 10-Volt filament winding. The fat wire between them is probably that winding's center tap.

I'll see what turns up at work tomorrow.

BTW I wouldn't put too much trust in the 1983-dated filter capacitors in the pic.

73

 

[238]

This is what is going back in it. I bought ever thing to overhaul a SSB220 years ago. I have bought the diodes & resisters to rebuild the diode board. If i remember correctly it only checked at 2200 volts. I thought if i rebuild the power supply it might pep up the voltage to the tube. 238

 

[238]

Got a ? about the green wires. One goes to ground the other goes to a diode. A cap hooks to the other end & goes to ground. Also 2 wires solder to the other end & each go to lights on the front an nothing else. The single black wire is solder to the green wire from the transformer. 238

 

[238]

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[238]

This is the new parts installed Hope to try it out to night. 238

 

[nomadradio]

Don't know if yours is keyed from a foot-switch jack on the rear, or if has carrier-sensing circuit to key whenever the radio feeds it a carrier.

The diode and cap above should be there to power the antenna relay in the rear.

73

 

[238]

Traded from this amp in Il. about 25 years ago. Never tried it out. When i got it home, haul it home in the sleeper off my big truck, it would not key. Was not a place for a foot petal to plug in. Took to to a friend an opened it up. There was no keying broad in it. He put me one in. You can see it in the top left corner. 238

 

[nomadradio]

Whups!

I thought the amplifier is a JB2000. Doesn't look like one.

Bear in mind that if this amp has two tubes you need to wire the filaments in series, since this is what the transformer's filament winding is built to match. The cathode choke has a third skinny wire that attaches to the center point between the two filaments, wound around the fat wires on the cathode choke, and then connected to the center tap of the 10-Volt filament winding.

If this amplifier's tube sockets have the filaments wired in parallel, you need to reconfigure them to match this transformer.

73

 

[BJ radionut]

I thought he said this was a single tube 3-500z? The partial picture of the RF deck looks like a single tuber.
He said this is the 3rd transformer in this amplifier(SB220 first and JB2000 last) both of which went up in smoke. (?)
Interesting since either of those should have been adequate to run a Single with headroom to spare.
Not sure why this is eating transformers.
The cooling fan looks to be a way too far away from the tube to give good pressure around the glass and socket base unless there is a shroud missing to focus the air across the tube and under the socket.
Hard to say since I am guessing this a partially disassembled project. Does the picture also seem to show the output coax attached to the end of the tank coil (?) maybe a P-L net?
Hard to tell from the partial picture, maybe he will post further pictures,
All the Best
Gary

PS: He also noted that the Plate Voltage was around 2200vdc, which on an SB220 transformer would be the low CW tap, the SSB position should be closer to 3000vdc.(+/-) Think the old JB2000 transformer should have been similar. (been a looong time since I have had my probes in one of those)

 

[238]

I thought i had put the whole story about this amp on here, but i see i did not. When i got it there where 2 6lq6 tubes driving the 3-500z. But you could not tune them separate , an the tuners for the 6lq6s where on the back. So i had the 6lq6s disconnected. The SSB transformer passed away an i replaced it with JB2000. I AM NOT a teck so i was told the JB did not put out as much voltage as the 220. Maybe when my friend put the JB transformer in it he did not wire it for high voltage so it would last me longer. I have had a JB 2000 before an they where tuff. It has a cover that covers the whole tube section front to back. I am moving the fan back to the middle an sealing the tube section up tight. 238

 

[BJ radionut]

Just to give you an idea of how parts placement looks on a similar amp.
I do not know this builder or standby his work but clean looking chassis set-up which is similar to yours. Just for reference on how things layout and general reference in layout.
Though I do question getting 2KW out of a single tube...proper operation should be more like 800 PEP but that's me.

 

[443]

Looks like his meter was out of Cal. Not sitting on 0 (the bird meter, not Daiwa). I'd go for 1500-1800PEP from a monobanded 3-500Z amp at 3KV and glowing like that. Can't say how long tube would last though. Run that amp at 1000-1200, last long time.

 

[nomadradio]

There are two JB2000 transformers that I know of. One of them provides only 2200 Volts DC from the HV. That one was meant for the 'low-drive' version that had a single 8417 driver tube. This kept the anode voltage for that tiny driver tube down (!) to 1100 Volts. Never mind the spec sheet for that tube says max 500 Volts. Black Cat amplifiers are more about steroids and less about longevity.

The other version with the 80-10 meter band switch and the two Z tubes had a transformer produced between 2700 and 3000 Volts DC.

We put fixed bias on any Z that runs from more than 2200 Volts. A series string of rectifier diodes wired for forward bias gets you about 2/3 of a Volt per diode. A series sting of 30 diodes will hold the zero-signal current of a 3-500Z down to 10 or 20 mA with no drive.

Simple rule is to use one diode for every 100 Volts of anode supply. This makes life easier on the tube when used for AM. And if sideband is your main interest, a higher zero-signal current is not a problem, and will probably improve audio quality a bit. Having no bias at all with 2200 Volts is about right for sideband, and should be okay on AM unless you plan to gouge it.

One drawback is that putting bias on the tube raises the tube's input impedance. If the amplifier has just a capacitor between the input side of the relay and the tube's cathode, this will call for adding a matching circuit. The input impedance of an amplifier really should be as close to 50 ohms as you can make it. This also tends to improve stability as well.

And if it ain't broke once you have high voltage again, it might be time to stop fixing it.

Remember the rule of the shad tree: "If it ain't broke, keep fixing it until it is".

One last thought. The tube socket must have some air flow across it. Doesn't have to be a hurricane, a gentle breeze is fine. Without this, the socket tends to overheat the two pins feeding 5 Volts into the filament. When the solder melts, the tube is on a downhill roll that can't be halted. The tube pin with the melted solder now begins to produce even more heat, and will darken the shiny contact surface of the socket's spring contacts. This increases the resistance of the filament circuit, releasing even more heat to melt more solder from inside the tube pin.

Downhill snowball. When the bad tube finally just won't light up the filament any more and gets replaced the new tube goes bad fairly soon because of the burned spring contact in the socket. Now the socket gets replaced, but the bad tube gets put back in. Ruins the new socket, the tube goes dark and another good tube is put into the new, but damaged socket.

Lather, rinse, repeat.

A good tube with the solder still intact inside the pins and a socket with bright, shiny contact surfaces will be fine, but only with that breeze directed across the underside of the socket.

73

 

[238]

I have both your diode broads.SSB220 & JB2000 just never used them yet. Got the amp back together & it is working. Looks to be around 2500 or better. Hard to tell my probe goes to 40K, but the needle is between 2 &3 K. One switch on the front says AM/AM+ One side goes to ground the other goes to the stud mounted diode on the back panel by the relay. The diode is also goes to the relay. On AM the switch is open & on AM+ it grounds the diode. AM+ gives it more watts. 238